Method for producing a hydrogenated block copolymer, hydrogenated block copolymer obtained by said production method and composition thereof

ABSTRACT

The present invention relates to a method for producing a hydrogenated block copolymer, comprises the steps of: (a) forming a block copolymer by allowing a living polymer having a specific structure to react with a bis-silane coupling agent having a specific structure; (b) hydrogenating the block copolymer to form a hydrogenated block copolymer; and (c) isolating the resultant hydrogenated block copolymer, in which the number of functional groups derived from the coupling agent in the hydrogenated block copolymer isolated in the step (c) is 1.5 or less per block copolymer molecule; a hydrogenated block copolymer obtained by the method; and a composition containing the hydrogenated block copolymer.

TECHNICAL FIELD

The present invention relates to a method for producing a hydrogenatedblock copolymer, a hydrogenated block copolymer obtained by the methodsand a composition containing the hydrogenated block copolymer.

BACKGROUND ART

Conventionally, there is known, as a production method for ahydrogenated block copolymer, a method involving forming a blockcopolymer by allowing a living polymer having an active terminal forliving anion polymerization to react with a coupling agent andhydrogenating the block copolymer (Patent Documents 1 to 3). Suchproduction method using a coupling agent has an advantage in that thesize of a polymer block can be easily controlled to performpolymerization at a low solution viscosity. In addition, when a couplingagent having three or more functional groups is used as the couplingagent, a branched radial-type block copolymer can be obtained, and theradial-type block copolymer is known to be excellent in flowability ascompared with a linear polymer having the same molecular weight.

CITATION LIST Patent Literature

[Patent Document 1] JP 2006-528721 W

[Patent Document 2] JP 2001-163934 A

[Patent Document 3] JP 08-208781 A

SUMMARY OF INVENTION Technical Problem

However, the production method for a radial-type block copolymer througha coupling reaction, as disclosed in each of Patent Documents 1 to 3,was found to have a problem in that an isolated hydrogenated blockcopolymer was liable to contain a large amount of a transition metal. Ifthe transition metal content in the hydrogenated block copolymer islarge, a composition to be obtained therefrom by kneading may turnyellow, which is not preferred. In the above-mentioned Patent Documents,no study has been made on means for reducing the transition metalcontent in the hydrogenated block copolymer.

Solution to Problem

The inventors of the present invention have made extensive studies andas a result have found that, in the case where unreacted functionalgroups are present in a coupling agent residue present in the center ofan isolated hydrogenated block copolymer, the functional groups eachinteract with a metal catalyst used for a hydrogenation reaction or thelike, with the result that a large amount of a transition metal iscontained in the hydrogenated block copolymer. Such unreacted functionalgroups may be produced in, for example, the case where a branching indexis lowered because of large steric hindrance of a living polymer used inthe coupling reaction et al. Further, the inventors of the presentinvention have further made extensive studies to solve the problem, andas a result have found that the problem can be solved by using acoupling agent having a specific structure to adjust the number offunctional groups derived from the coupling agent in a hydrogenatedblock copolymer after an isolating step to 1.5 or less per blockcopolymer molecule, thus completing the present invention.

That is, the invention of the present application provides the followingitems [1] to [10].

[1] A method for producing a hydrogenated block copolymer, comprisingthe steps of:

(a) forming a block copolymer by allowing a living polymer representedby formula (I):

P—X  (I)

where: P represents a copolymer chain having one or more aromatic vinylcompound polymer blocks (A) and one or more conjugated diene polymerblocks (B); and X represents an active terminal of a living anionpolymer, to react with a coupling agent represented by formula (II):

R¹ _(m)Y_(3-m)Si-A-SiY_(3-m)R¹ _(m)  (II)

where: R¹'s each independently represent an aryl group having 6 to 12carbon atoms, a linear or branched alkyl group having 1 to 12 carbonatoms, or a hydrogen atom; Y's each independently represent a fluorineatom, a chlorine atom, a bromine atom, an iodine atom, an alkoxy group,a carboxyl group, or a carboxylic acid ester group; A represents asingle bond or a linear alkylene group having 1 to 20 carbon atoms; andm represents 0 or 1;

(b) hydrogenating the block copolymer to form a hydrogenated blockcopolymer; and

(c) isolating the resultant hydrogenated block copolymer,

in which a number of functional groups derived from the coupling agentin the hydrogenated block copolymer isolated in the step (c) is 1.5 orless per block copolymer molecule.

[2] The method for producing a hydrogenated block copolymer according tothe above-mentioned item [1], in which the Y's represent alkoxy groupsrepresented by OR²'s, where R²'s each independently represent a linearor branched alkyl group having 1 to 12 carbon atoms.

[3] The method for producing a hydrogenated block copolymer according tothe above-mentioned item [2], in which the coupling agent includes abisdialkoxyalkylsilylalkane.

[4] The method for producing a hydrogenated block copolymer according tothe above-mentioned item [3], in which the coupling agent comprisesbisdiethoxymethylsilylehtane.

[5] The method for producing a hydrogenated block copolymer according toany one of the above-mentioned items [1] to [4], in which the functionalgroups derived from the coupling agent in the hydrogenated blockcopolymer comprise hydroxyl groups which are bonded directly to Siatoms.

[6] The method for producing a hydrogenated block copolymer according toany one of the above-mentioned items [1] to [5], further comprising thestep of (d) deactivating an unreacted functional group Y present in acoupling agent residue in the block copolymer or the hydrogenated blockcopolymer prior to the step (c).

[7] The method for producing a hydrogenated block copolymer according toany one of the above-mentioned items [1] to [6], in which thehydrogenated block copolymer has a branching index of 2.3 or more.

[8] A hydrogenated block copolymer, comprising a copolymer representedby general formula P′ and/or (P′)_(n)—Z, where: P′ represents acopolymer chain having one or more aromatic vinyl compound polymerblocks (A) and one or more hydrogenated conjugated diene polymer blocks(B); Z represents part of a silane coupling agent represented by formula(II):

R¹ _(m)Y_(3-m)Si-A-SiY_(3-m)R¹ _(m)  (II)

where: R¹'s each independently represent an aryl group having 6 to 12carbon atoms, a linear or branched alkyl group having 1 to 12 carbonatoms or a hydrogen atom; Y's each independently represent a fluorineatom, a chlorine atom, a bromine atom, an iodine atom, an alkoxy group,a carboxyl group or a carboxylic acid ester group; A represents a singlebond or a linear alkylene group having 1 to 20 carbon atoms; and mrepresents 0 or 1; and n represents an integer of 1 to 6, in which thehydrogenated block copolymer has a branching index of 2.3 or more and atransition metal content of 100 ppm or less.

[9] The hydrogenated block copolymer according to the above-mentioneditem [8], which is obtained by the method according to any one of theabove-mentioned items [1] to [7].

[10] A thermoplastic elastomer composition, comprising: the hydrogenatedblock copolymer according to the above-mentioned item [8] or [9]; and anon-aromatic rubber softener at a ratio of 1 to 2,000 parts by mass withrespect to 100 parts by mass of the hydrogenated block copolymer.

Advantageous Effects of Invention

According to the present invention, it is possible to provide theradial-type hydrogenated block copolymer having a low transitional metalcontent and the method for producing the same.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention is described in detail.

A method of the present invention is a method for producing ahydrogenated block copolymer, including the steps of:

(a) forming a block copolymer by allowing a living polymer having aspecific structure to react with a bis-silane coupling agent having aspecific structure;

(b) hydrogenating the block copolymer to form a hydrogenated blockcopolymer; and

(c) isolating the resultant hydrogenated block copolymer, in which thenumber of functional groups derived from the coupling agent in thehydrogenated block copolymer isolated in the step (c) is 1.5 or less perblock copolymer molecule.

[Step (a)]

The living polymer used in the step (a) of preparing a block copolymeris a living polymer represented by formula (I):

P—X  (I)

where P represents a copolymer chain having one or more aromatic vinylcompound polymer blocks (A) and one or more conjugated diene polymerblocks (B); and X represents an active terminal of a living anionpolymer.

The polymer block (A) in the copolymer chain P mainly comprises astructural unit derived from an aromatic vinyl compound (aromatic vinylcompound unit). Here, the term “mainly” means that the aromatic vinylcompound unit is contained in an amount of preferably 70% by mass ormore, more preferably 90% by mass or more, still more preferably 100% bymass based on the mass of the polymer block (A).

Examples of the aromatic vinyl compound comprised in the polymer block(A) include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene,4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene,2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, 1-vinylnaphthalene and2-vinylnaphthalene.

The polymer block (A) may comprise only a structural unit derived fromone kind of the aromatic vinyl compounds or may comprise structuralunits derived from two or more kinds thereof. Among them, it ispreferred that the polymer block (A) mainly comprises a structural unitderived from styrene or α-methylstyrene.

The polymer block (A) may include a small amount of a structural unitderived from an additional copolymerizable monomer together with thestructural unit derived from the aromatic vinyl compound. In this case,the amount of the structural unit derived from the additionalcopolymerizable monomer is preferably less than 30% by mass, morepreferably less than 10% by mass based on the mass of the polymer block(A).

Examples of the additional copolymerizable monomer include anionicallypolymerizable monomers such as a methacrylate ester, an acrylate ester,1-butene, pentene, hexene, 1,3-butadiene, isoprene, and methyl vinylether. The bonding form of the units based on these additionalcopolymerizable monomer may be any form such as a random or taperedform.

The polymer block (B) in the copolymer chain P mainly comprises astructural unit derived from a conjugated diene (conjugated diene unit).Here, the term “mainly” means that the conjugated diene unit iscontained in an amount of preferably 70% by mass or more, morepreferably 90% by mass or more, still more preferably 100% by mass basedon the mass of the polymer block (B).

Examples of the conjugated diene comprised in the polymer block (B)include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene and 1,3-hexadiene.

The polymer block (B) may comprise only a structural unit derived fromone kind of the conjugated dienes or may comprise structural unitsderived from two or more kinds thereof. Among them, it is preferred thatthe polymer block (B) mainly comprises structural units derived from1,3-butadiene, isoprene or a mixture of 1,3-butadiene and isoprene, morepreferred that the polymer block (B) mainly comprises structural unitsderived from a mixture of 1,3-butadiene and isoprene. In the case wherethe polymer block (B) has structural units derived from two or morekinds of conjugated dienes, the bonding form of the units may be arandom, block, or tapered form, or a combination of two or more kindsthereof.

The polymer block (B) may include a small amount of a structural unitderived from an additional copolymerizable monomer together with thestructural unit derived from the conjugated diene to the extent that theobject of the present invention is not impaired. In this case, theamount of the structural unit derived from the additionalcopolymerizable monomer is preferably less than 30% by mass, morepreferably less than 10% by mass based on the mass of the polymer block(B).

Examples of the additional copolymerizable monomer include anionicallypolymerizable monomers which are aromatic vinyl compounds such asstyrene, α-methylstyrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, 1,3-dimethylstyrene, diphenylethylene,1-vinylnaphthalene, 4-propylstyrene, 4-cyclohexylstyrene,4-dodecylstyrene, 2-ethyl-4-benzyl styrene and 4-(phenylbutyl)styrene.Those additional copolymerizable monomers may be used alone or incombination of two or more kinds thereof. In the case ofcopolymerization of the structural unit derived from the conjugateddiene and the structural unit derived from the additionalcopolymerizable monomer such as the aromatic vinyl compound, the bondingform of the units may be any of random and tapered forms.

The polymer block (B) is hydrogenated in the step of hydrogenation. Fromthe viewpoint of heat resistance and weather resistance, in thehydrogenated polymer block (B) in the hydrogenated block copolymer ofthe present invention, carbon-carbon double bonds derived from theconjugated diene are hydrogenated at a ratio of preferably 50% or more,more preferably 80% or more, still more preferably 90% or more. Here,the hydrogenation degree may be determined from measured values obtainedby measuring the contents of the carbon-carbon double bonds derived fromthe conjugated diene unit in the polymer block (B) before and after thehydrogenation by iodine value measurement, infrared spectrophotometer,¹H-NMR spectrum, or the like.

The bonding forms (microstructures) of the structural unit derived fromthe conjugated diene in the polymer block (B) and the abundance ratiosthereof are not particularly limited. For example, a unit derived from1,3-butadiene may have a bonding form of a 1,2-bond (vinyl bond) or a1,4-bond, and a unit derived from isoprene may have a bonding form of a1,2-bond (vinyl bond), a 3,4-bond (vinyl bond), or a 1,4-bond. Only onekind of these bonding forms may be present, or two or more kinds thereofmay be present. Further, any of the bonding forms may be present at anyratio. Moreover, in the case where the polymer block (B) comprises onlya structural unit derived from 1,3-butadiene, the amount of the 1,2-bond(amount of the vinyl bond) is preferably adjusted to 25% or more inorder to prevent deterioration of the performance of the elastomer bycrystallization caused after hydrogenation.

The copolymer chain P has one or more polymer blocks (A) and one or morepolymer blocks (B). The bonding form of the polymer block (A) andpolymer block (B) is not particularly limited and may be any of linear,branched and radial forms, or a bonding form of a combination of two ormore thereof. The content of the polymer blocks (A) is preferably 5 to70% by mass, more preferably 10 to 55% by mass, particularly preferably15 to 45% by mass with respect to the total amount of the hydrogenatedblock copolymer. In the case where the content of the polymer blocks (A)is less than 5% by mass, the resultant thermoplastic elastomercomposition may have poor heat resistance. While in the case where thecontent exceeds 70% by mass, it is not preferred by reason that thehydrogenated block copolymer is liable to have an excessively high meltviscosity, resulting in poor processability, and the resultantthermoplastic elastomer composition may have poor flexibility, which isnot preferred.

When the polymer block (A) and polymer block (B) are represented by Aand B, respectively, specific examples of the copolymer chain include adiblock type represented by [A-B-] or [B-A-], a triblock typerepresented by [A-B-A-] or [B-A-B-], a tetrablock type represented by[A-B-A-B-] or [B-A-B-A-], or a polyblock type formed by linearly bonding5 or more of A('s) and B('s). Among them, the diblock type representedby [A-B-] and the triblock type represented by [A-B-A-] or [B-A-B-] arepreferred in which the polymer blocks (A) (hard block) are bonded viathe polymer block (B) (soft block) in a block copolymer after a couplingreaction, resulting in excellent rubber elasticity.

The copolymer chain P may have one kind or two or more kinds offunctional groups such as a carboxyl group, a hydroxyl group, an acidanhydride group, an amino group and an epoxy group in the molecularchain and/or at the end of the molecular chain as long as the object andeffect of the present invention are not prevented. In addition, thefunctional groups may be introduced into the block copolymer after acoupling reaction or a hydrogenation reaction. As a method forproducing, there is given, for example, a method to be reacted withmaleic anhydride.

In the hydrogenated block copolymer of the present invention, themolecular weights of the polymer block (A) and polymer block (B) are notparticularly limited. However, from the viewpoint of heat resistance andprocessability of the resultant thermoplastic elastomer composition, theweight-average molecular weight of each polymer block (A) is preferably3,000 to 100,000, more preferably 5,000 to 70,000, and theweight-average molecular weight of each polymer block (B) is preferably5,000 to 400,000, more preferably 10,000 to 200,000.

The weight-average molecular weight of the living polymer beforehydrogenation is preferably 8,000 to 500,000, more preferably 15,000 to300,000. If the weight-average molecular weight of the living polymer islarger than the range, the branching index may become small to increasethe number of unreacted functional groups. Here, the weight-averagemolecular weight of the living polymer may be estimated to be almost thesame value as the weight-average molecular weight of an uncoupledpolymer component.

The weight-average molecular weight of the whole hydrogenated blockcopolymer is preferably 16,000 or more, more preferably 30,000 or more,still more preferably 50,000 or more, most preferably 60,000 or more.Further, the weight-average molecular weight of the whole hydrogenatedblock copolymer is preferably 1,000,000 or less, more preferably 800,000or less, still more preferably 600,000 or less. If the weight-averagemolecular weight of the hydrogenated block copolymer is less than16,000, the resultant thermoplastic elastomer composition may haveinsufficient heat resistance, while if the weight-average molecularweight exceeds 1,000,000, the resultant thermoplastic elastomercomposition may have poor processability.

It should be noted that the term “weight-average molecular weight” asused herein means a weight-average molecular weight in terms ofpolystyrene determined by gel permeation chromatography (GPC)measurement.

The living polymer can be produced by a known polymerization method. Ingeneral, an intended living polymer can be obtained by sequentiallypolymerizing monomers using an alkyl lithium compound as an initiator inan inert solvent.

Examples of the alkyl lithium compound include methyl lithium, ethyllithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium andpentyl lithium.

The polymerization is preferably preformed in the presence of a solvent.The solvent is not particularly limited as long as the solvent is inertto the initiator and has no adverse effect on the reaction, and examplesthereof include saturated aliphatic hydrocarbons and aromatichydrocarbons, such as hexane, cyclohexane, heptane, octane, decane,toluene, benzene and xylene. In addition, the polymerization reaction isusually performed at a temperature ranging from 0 to 100° C. for 0.5 to50 hours.

Further, a Lewis base may be used as a co-catalyst during thepolymerization. Examples of the Lewis base include: ethers such asdimethyl ether, diethyl ether and tetrahydrofuran; glycol ethers such asethylene glycol dimethyl ether and diethylene glycol dimethyl ether; andamines such as triethylamine, N,N,N′,N′-tetramethylethylenediamine andN-methylmorpholine. One kind of those Lewis bases may be used alone, ortwo or more kinds thereof may be used.

The coupling agent to be used in the method of the present invention isa coupling agent represented by formula (II):

R¹ _(m)Y_(3-m)Si-A-SiY_(3-m)R¹ _(m)  (II)

where: R¹'s each independently represent an aryl group having 6 to 12carbon atoms, a linear or branched alkyl group having 1 to 12 carbonatoms or a hydrogen atom; Y's each independently represent a fluorineatom, a chlorine atom, a bromine atom, an iodine atom, an alkoxy group,a carboxyl group or a carboxylic acid ester group; A represents a singlebond or a linear alkylene group having 1 to 20 carbon atoms; and mrepresents 0 or 1.

When a bis-silyl compound represented by formula (II) is used as acoupling agent, it is possible to suppress effects of steric hindranceand to increase the number of functional groups involved in the couplingreaction to reduce the number of unreacted functional groups.

Examples of the coupling agent represented by formula (II) include:alkoxy silane coupling agents such as bisdimethoxymethylsilylethane,bisdiethoxymethylsilylethane, bisdiethoxyethylsilylpentane,bisdibutoxymethylsilylethane, bistrimethoxysilylhexane,bistriethoxysilylethane and bistripropoxysilylpentane; and halosilanecoupling agents such as bisdichloromethylsilylethane,bisdibromoethylsilylhexane, bisdibromopropylsilylheptane,bistrichlorosilylethane and bistribromosilylhexane.

From the viewpoint of environment safety and reactivity, the couplingagent is preferably a compound having an alkoxy group as a functionalgroup. Therefore, among the coupling agent represented by formula (II),Y's (hereinafter, sometimes referred to as functional groups Y) arepreferably alkoxy groups represented by OR² (where R²'s eachindependently represent a linear or branched alkyl group having 1 to 12carbon atoms). That is, the coupling agent is preferably a couplingagent represented by formula (III):

R₁ _(m)(OR²)_(3-m)Si-A-Si(OR²)_(3-m)R¹ _(m)  (III)

where R¹'s each independently represent an aryl group having 6 to 12carbon atoms, a linear or branched alkyl group having 1 to 12 carbonatoms or a hydrogen atom; R²'s each independently represent a linear orbranched alkyl group having 1 to 12 carbon atoms; A represents a singlebond or a linear alkylene group having 1 to 20 carbon atoms; and mrepresents 0 or 1.

Examples of the coupling agent in which the functional groups Yrepresent alkoxy groups (coupling agent represented by formula (III))include bisalkoxysilylalkane compounds such asbisdimethoxymethylsilylethane, bisdiethoxymethylsilylethane,bisdiethoxyethylsilylpentane, bisdibutoxymethylsilyl ethane,bistrimethoxysilylhexane, bistriethoxysilylethane andbistripropoxysilylpentane. Among them, bisdiethoxymethylsilylethane andbistriethoxysilylethane are preferred.

The number of the functional groups Y included per molecule of thecoupling agent is preferably 4 to 6, more preferably 4 to 5. As thenumber of the functional groups Y becomes larger, the resultant polymertends to more easily form a radial structure. On the other hand, as thenumber of the functional groups Y becomes smaller, the number ofunreacted functional groups in a coupling residue after the couplingreaction becomes smaller. Therefore the number of functional groupsderived from the coupling agent in the hydrogenated block copolymerobtained as a final product tends to decrease, which enables omission ofthe step of deactivating the functional groups Y or reduction of theamount of a reagent added for deactivating the functional groups Y.

In order to adjust the number of the functional groups Y included percoupling agent molecule to a preferred range, a compound initiallyhaving a desired number of the functional groups may be used, or part ofthe functional groups of a compound having the functional groups largerthan desired number may be deactivated previously before use.

Examples of the reagent used for deactivating part of the functionalgroups Y in the coupling agent previously include Lewis bases including:alkyl lithiums such as methyl lithium, ethyl lithium, n-propyl lithium,isopropyl lithium, n-butyl lithium, sec-butyl lithium and t-butyllithium; alkyl sodiums such as methyl sodium, ethyl sodium, n-propylsodium, isopropyl sodium, n-butyl sodium, sec-butyl sodium and t-butylsodium; alkyl potassiums such as methyl potassium, ethyl potassium,n-propyl potassium, isopropyl potassium, n-butyl potassium, sec-butylpotassium and t-butyl potassium; alkyl magnesium halides such as methylmagnesium bromide, ethyl magnesium bromide, t-butyl magnesium chlorideand sec-butyl magnesium iodide; dialkyl copper lithiums such as dimethylcopper lithium, diethyl copper lithium, methyl ethyl copper lithium,methyl n-propyl copper lithium and ethyl n-butyl copper lithium; andlithium amides such as lithium diisopropyl amide, lithium diisoethylamide and lithium di-t-butyl amide.

Among them, methyl lithium, methyl magnesium bromide and dimethyl copperlithium are preferred because steric hindrance of the coupling agentafter deactivation is small in the coupling reaction.

The amount of the coupling agent is very important in determining thenumber of arms in the radial structure. The molar ratio of the couplingagent to an active terminal is independent of the number of functionalgroups in the coupling agent and is preferably 0.1 to 0.5, morepreferably 0.2 to 0.4. If the molar ratio of the coupling agent to theactive terminal is less than 0.1, many radial structures having manyarms are produced, but the coupling efficiency becomes low because theamount of the coupling agent is small. On the other hand, if the molarratio of the coupling agent to the active terminal is larger than 0.5,the coupling efficiency becomes high, but polymers each having theradial structure are hardly produced because many two-arm polymers(linear polymers) are produced.

Meanwhile, the coupling reaction is usually performed at a temperatureranging from 0 to 100° C. for 0.5 to 50 hours. The coupling agent may bediluted before use, and a solvent for dilution is not particularlylimited as long as the solvent is inert to the active terminal and hasno adverse effect on the reaction. Examples thereof include saturatedaliphatic hydrocarbons and aromatic hydrocarbons, such as hexane,cyclohexane, heptane, octane, decane, toluene, benzene and xylene.Further, in the coupling reaction, a Lewis base may be added as anadditive, and examples of the Lewis base include ethers such as dimethylether, diethyl ether and tetrahydrofuran; glycol ethers such as ethyleneglycol dimethyl ether and diethylene glycol dimethyl ether; and aminessuch as triethylamine, N,N,N′,N′-tetramethylethylenediamine andN-methylmorpholine. One kind of those Lewis bases may be used alone, ortwo or more kinds thereof may be used in combination.

The coupling ratio in a reaction of the living polymer with the couplingagent is preferably 50% or more, more preferably 60% or more, still morepreferably 70% or more. If the coupling ratio is less than 50%, thestrength of the resultant thermoplastic elastomer composition decreases,which is not preferred.

By using elution curves which are obtained by gel permeationchromatography (GPC), it is possible to obtain the coupling ratio bydividing a peak area of a polymer produced by coupling by the sum of thepeak area of the polymer produced by coupling and a peak area of anuncoupled polymer. That is, the coupling ratio can be determined by thefollowing equation.

Coupling ratio(%)=(peak area of polymer produced by coupling)/(sum ofpeak area of polymer produced by coupling and peak area of uncoupledpolymer)×100

The coupling ratio can be increased by increasing the amount of thecoupling agent added, raising the reaction temperature, or lengtheningthe reaction time.

The branching index of the hydrogenated block copolymer is preferably2.3 or more, more preferably 2.4 or more, still more preferably 2.6 ormore. The term “branching index” herein refers to a index determined bydividing the weight-average molecular weight (Mw) of a polymer producedby coupling by the weight-average molecular weight (Mw) of an uncoupledpolymer, which are determined by gel permeation chromatography (GPC)measurement. That is, the branching index can be determined by thefollowing equation.

Branching index=(weight-average molecular weight (Mw) of polymerproduced by coupling)/(weight-average molecular weight (Mw) of uncoupledpolymer)

The branching index can be controlled by the number of functional groupseach capable of reacting with the active terminal of a living anionicpolymer of a coupling agent. In general, when a coupling agent havingmany functional groups each capable of reacting with the active terminalof the living anionic polymer is used, a block copolymer having a highbranching index can be obtained. When a coupling agent having three ormore functional groups each capable of reacting with the active terminalis used, the branching index can be increased to 2.3 or more. When thebranching index of the hydrogenated block copolymer is increased byusing a coupling agent having many functional groups, the number ofunreacted functional groups Y usually tends to become large after thecoupling reaction. Therefore, in the case of production of ahydrogenated block copolymer having a large branching index, the effectof the present invention can be exerted more effectively.

[Step (b)]

Coupling and hydrogenation may be performed successively, orhydrogenation may be performed after the block copolymer is isolatedonce.

In the case where the block copolymer is isolated, the block copolymermay be isolated by, after performing the polymerization by theabove-mentioned method, pouring the polymerization reaction solutioninto a poor solvent of the block copolymer such as methanol to solidifythe block copolymer, or pouring the polymerization reaction solutioninto hot water together with steam to remove the solvent by azeotropy(steam stripping) and drying the resultant product.

The hydrogenation reaction of the block copolymer can usually beperformed in the presence of a hydrogenation catalyst such as a Zieglercatalyst composed of a combination of a transition metal compound (suchas nickel octylate, nickel neodecanoate, nickel naphthenate, nickelacetylacetonate, cobalt octylate, cobalt neodecanoate, cobaltnaphthenate or cobalt acetylacetonate) and an organic aluminum compoundsuch as triethyl aluminum or triisobutyl aluminum or an organic lithiumcompound; or a metallocene catalyst composed of a combination of abis(cyclopentadienyl) compound of a transition metal such as titanium,zirconium or hafnium and an organic metal compound including lithium,sodium, potassium, aluminum, zinc, magnesium or the like, underconditions of a reaction temperature of 20 to 200° C., a hydrogenpressure of 0.1 to 20 MPa, and a reaction time of 0.1 to 100 hours.

[Step (c)]

In the case where coupling and hydrogenation are performed successively,the hydrogenated block copolymer may be isolated by pouring thehydrogenation reaction solution into a poor solvent of the hydrogenatedblock copolymer such as methanol to solidify the hydrogenated blockcopolymer, or pouring the hydrogenation reaction solution into hot watertogether with steam to remove the solvent by azeotropy (steam stripping)and drying the resultant product.

Before the isolation of the hydrogenated block copolymer, the polymersolution is washed with water to reduce the amount of a metal catalystin the isolated hydrogenated block copolymer. When washing is performedusing an acidic aqueous solution, the efficiency of washing can befurther improved. An acid to be used is preferably exemplified by amonovalent or polyvalent strong acid such as hydrochloric acid, nitricacid or sulfuric acid; a monovalent or polyvalent carboxylic acid suchas acetic acid, propionic acid, succinic acid or citric acid; and amonovalent or polyvalent weak acid such as carbonic acid or phosphoricacid.

[Step (d)]

The production method of the present application effectively andpreferably includes (d) the step of deactivating unreacted functionalgroups Y present in a coupling agent residue in the block copolymer orthe hydrogenated block copolymer prior to the step (c) as a means toreducing the number of functional groups present in the hydrogenatedblock copolymer.

The unreacted functional groups Y present in the coupling agent residuein the hydrogenated block copolymer may react with water or an acidadded in the isolating step (c) to produce hydroxyl groups, which mayinteract with a metal catalyst. Therefore, the deactivation step (d) ispreferably performed before the isolating step (c).

That is, in the production method of the present invention, the step (d)may be omitted as long as the number of the unreacted functional groupsY present in the coupling agent residue in the hydrogenated blockcopolymer isolated in the isolating step (c) (residual functionalgroups) is 1.5 or less. In the case where the method includes the step(d), the order of “step (a)→step (d)→step (b)→step (c)” may be adopted,or the order of “step (a)→step (b)→step (d)→step (c)” may be adopted.

Examples of the reagent used for deactivating the functional groups Y(hereinafter, sometimes referred to as deactivating reagent) includeLewis bases including: alkyl lithiums such as methyl lithium, ethyllithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyllithium and t-butyl lithium; alkyl sodiums such as methyl sodium, ethylsodium, n-propyl sodium, isopropyl sodium, n-butyl sodium, sec-butylsodium and t-butyl sodium; alkyl potassiums such as methyl potassium,ethyl potassium, n-propyl potassium, isopropyl potassium, n-butylpotassium, sec-butyl potassium and t-butyl potassium; alkyl magnesiumhalides such as methyl magnesium bromide, ethyl magnesium bromide,t-butyl magnesium bromide, t-butyl magnesium chloride and sec-butylmagnesium iodide; dialkyl copper lithiums such as dimethyl copperlithium, diethyl copper lithium, methyl ethyl copper lithium, methyln-propyl copper lithium and ethyl n-butyl copper lithium; and lithiumamides such as lithium diisopropyl amide, lithium diisoethyl amide andlithium di-t-butyl amide.

Among them, methyl lithium, methyl magnesium bromide and dimethyl copperlithium are preferred because steric hindrance is desirably small toprogress the deactivation reaction rapidly.

The molar ratio of the amount of the deactivating reagent used in thestep (d) to the functional groups Y remaining in the coupling agentresidue in the copolymer after the coupling reaction is preferably 0.5or more, more preferably 1.0 or more and is preferably 100 or less, morepreferably 50 or less. In the case where the amount of the deactivatingreagent is insufficient, the number of the residual functional groupstends not to become 1.5 or less, resulting in increasing the transitionmetal content in a hydrogenated block copolymer obtained as a finalproduct.

The deactivation reaction of the functional groups Y is usuallyperformed at a temperature ranging from 0 to 100° C. for 0.1 to 50hours. The deactivating reagent may be diluted before use, and a solventfor dilution is not particularly limited as long as the solvent is inertto the deactivating reagent and has no adverse effect on the reaction.Examples thereof include saturated aliphatic hydrocarbons and aromatichydrocarbons, such as hexane, cyclohexane, heptane, octane, decane,toluene, benzene and xylene. Further, in the deactivation reaction ofthe functional groups Y, a Lewis base may be added as an additive, andexamples of the Lewis base include: ethers such as dimethyl ether,diethyl ether and tetrahydrofuran; glycol ethers such as ethylene glycoldimethyl ether and diethylene glycol dimethyl ether; and amines such astriethylamine, N,N,N′,N′-tetramethylethylenediamine andN-methylmorpholine. One kind of those Lewis bases may be used alone, ortwo or more kinds thereof may be used in combination.

[Hydrogenated Block Copolymer]

The hydrogenated block copolymer obtained by the production method ofthe present invention is a hydrogenated block copolymer including acopolymer represented by general formula P′ and/or (P′)_(n)—Z and havinga branching index of 2.3 or more and a transition metal content of 100ppm or less. Here, P′ represents a copolymer chain having one or morearomatic vinyl compound polymer blocks (A) and one or more hydrogenatedconjugated diene polymer blocks (B), Z represents part of a silanecoupling agent represented by the formula (II), and n represents aninteger of 1 to 6.

That is, the hydrogenated block copolymer of the present invention is amixture of:

-   (1) a radial-type hydrogenated block copolymer having six arms,    which is represented by general formula (P′)₆—Z;-   (2) a radial-type hydrogenated block copolymer having five arms,    which is represented by general formula (P′)₅—Z;-   (3) a radial-type hydrogenated block copolymer having four arms,    which is represented by general formula (P′)₄—Z;-   (4) a radial-type hydrogenated block copolymer having three arms,    which is represented by general formula (P′)₃—Z;-   (5) a linear hydrogenated block copolymer having two arms, which is    represented by general formula (P′)₂—Z;-   (6) a linear hydrogenated block copolymer having one arm, which is    represented by general formula P′—Z; and-   (7) a linear hydrogenated block copolymer represented by general    formula P′. It should be noted that component ratios of the    copolymers (1) to (7) in the hydrogenated block copolymer of the    present invention may be appropriately determined depending on the    types of the living polymer used as a raw material and the silane    coupling agent, and reaction conditions.

[Number of Residual Functional Groups in Hydrogenated Block Copolymer]

In the production method of the present invention, it is important thatthe number of functional groups derived from the coupling agent in theresultant hydrogenated block copolymer (residual functional groups) be1.5 or less, preferably 1.3 or less per block copolymer molecule. Thephrase “functional groups derived from the coupling agent” as usedherein include functional groups remaining in the coupling agent withoutany reactions and hydroxyl groups produced by hydrolysis of thefunctional groups in the coupling agent. If the number of the residualfunctional groups is 1.5 or less, an interaction between each of theresidual functional groups and a metal catalyst used for a hydrogenationreaction et al. can be suppressed, allowing production of a hydrogenatedblock copolymer having a low transition metal content. The number of theresidual functional groups can be reduced by using a coupling agenthaving a small number of functional groups or by deactivating unreactedfunctional groups after the coupling reaction. In addition, the numberof the residual functional groups can be adjusted by reducing the amountof the coupling agent with respect to the living polymer. In the casewhere the amount of the coupling agent with respect to the livingpolymer is small, the ratio of the living polymer to the number of thefunctional groups becomes larger, allowing production of a hydrogenatedblock copolymer having a large branching index, i.e., allowing reductionof the number of the residual functional groups derived from thecoupling agent. In this case, the coupling efficiency is liable tobecome lower. Further, in the case of coupling of a living polymerhaving a small weight-average molecular weight, steric hindrance in thecoupling reaction becomes small, allowing production of a blockcopolymer having a large branching index, i.e., allowing reduction ofthe number of the residual functional groups derived from the couplingagent. In the case where a block copolymer having a large branchingindex is produced by the coupling reaction, if the number of theresidual functional groups derived from the coupling agent is 1.5 orless, a radial-type hydrogenated block copolymer having a low transitionmetal content can be produced without the deactivation step by theeffect of the present invention.

In the case where, of the residual functional groups, hydroxyl groupswhich are bonded directly to Si atoms produced by hydrolysis of thefunctional groups Y (silanol groups) interact with a transition metal,the transition metal is particularly sterically restricted, and hencethe transition metal content in the hydrogenated block copolymerobtained as a final product is affected. Therefore, it is important thatthe number of the silanol groups in the resultant hydrogenated blockcopolymer be 1.5 or less, preferably 1.3 or less per block copolymermolecule.

The number of the functional groups derived from the coupling agent(residual functional groups) can be determined from the results of²⁹Si-NMR measurement of a solution of the polymer in deuteratedchloroform. Specifically, the number can be calculated by summatingvalues obtained by multiplying integrated values of Si having noresidual functional group, Si having one residual functional group, Sihaving two residual functional groups, etc. by the number of thefunctional groups, and comparing the sum with the simple sum of theintegrated values. It should be noted that the results of ²⁹Si-NMRmeasurement are substantially unaffected by a change of the number ofprotons by hydrogenation, so the number of functional groups Y beforehydrogenation is calculated to be almost the same as the number ofresidual functional groups after hydrogenation.

[Transition Metal Content in Hydrogenated Block Copolymer]

According to the production method of the present invention, it ispossible to produce a hydrogenated block copolymer having a lowtransition metal content. Specifically, the transition metal contentmeasured by an atomic absorption method is preferably 100 ppm or less,more preferably 80 ppm or less, still more preferably 50 ppm or less. Ifthe transition metal content exceeds the above-mentioned range, in thecase where a thermoplastic elastomer composition is prepared by kneadingthe hydrogenated block copolymer together with another component, theresultant thermoplastic elastomer composition may turn yellow, which isnot preferred.

[Thermoplastic Elastomer Composition]

The thermoplastic elastomer composition of the present inventionincludes the above-mentioned hydrogenated block copolymer and anon-aromatic rubber softener. The term “non-aromatic rubber softener” asused herein refers to a rubber softener in which the number of carbonatoms in an aromatic ring accounts for less than 35% of the number ofcarbon atoms in the whole molecule.

The thermoplastic elastomer composition of the present invention maycomprise one kind of the hydrogenated block copolymer or a mixture oftwo or more kinds of the hydrogenated block copolymers.

Examples of the non-aromatic rubber softener include: mineral oils suchas a paraffin-based process oil and a naphthenic process oil; vegetableoils such as a peanut oil and a rosin; phosphoric acid esters;low-molecular-weight polyethylene glycol; liquid paraffins; andsynthetic oils such as low-molecular-weight ethylene, anethylene/α-olefin copolymerization oligomer, liquid polybutene, liquidpolyisoprene or a hydrogenated product thereof, and liquid polybutadieneor a hydrogenated product thereof. Among them, in view of compatibilitywith the hydrogenated block copolymer, a paraffin oil such as aparaffin-based process oil or a liquid paraffin is suitably used. Theterm “paraffin oil” as used herein refers to an oil in which the numberof carbon atoms in a paraffin chain accounts for 50% or more of thenumber of carbon atoms in the whole molecule. The paraffin oil has akinetic viscosity at 40° C. in the range of preferably 10 to 500 mm²/s,more preferably 15 to 400mm²/s, still more preferably 20 to 300 mm²/s.One kind of those softeners may be used alone, or two or more kindsthereof may be used in combination.

The non-aromatic rubber softener content in the thermoplastic elastomercomposition of the present invention is in the range of preferably 1 to2,000 parts by mass, more preferably 25 to 1,500 parts by mass, stillmore preferably 100 to 1,300 parts by mass with respect to 100 parts bymass of the hydrogenated block copolymer. In the case where the contentexceeds 2,000 parts by mass, the strength of the resultant thermoplasticelastomer composition is liable to become significantly lower.

In addition, with regard to the non-aromatic rubber softener content inthe thermoplastic elastomer composition of the present invention, thenon-aromatic rubber softener content with respect to the wholethermoplastic elastomer composition is preferably 1% by mass or more,more preferably 20% by mass or more, still more preferably 50% by massor more. In the case where the non-aromatic rubber softener content isless than 1% by mass, the moldability of the resultant thermoplasticelastomer composition is liable to become lower.

In the thermoplastic elastomer composition of the present invention, anadditional thermoplastic resin may be blended depending on the intendeduse. Examples of the thermoplastic resin include: polyolefin-basedresins including polypropylene, high-density polyethylene,medium-density polyethylene, low-density polyethylene, ethylene-α-olefincopolymers such as an ethylene-propylene copolymer, an ethylene-1-butenecopolymer, an ethylene-1-hexene copolymer, an ethylene-1-heptenecopolymer, an ethylene-1-octene copolymer, anethylene-4-methyl-1-pentene copolymer, an ethylene-1-nonene copolymerand an ethylene-1-decene copolymer, an ethylene-vinyl acetate copolymer,an ethylene-acrylic acid copolymer, an ethylene-acrylic acid estercopolymer, an ethylene-methacrylic acid copolymer, anethylene-methacrylic acid ester copolymer, and resins obtained bymodifying those polymers with maleic anhydride and the like;polystyrene-based resins such as polystyrene, poly-α-methylstyrene,poly-p-methylstyrene, an acrylonitrile-styrene resin, anacrylonitrile-butadiene-styrene resin, a maleic anhydride-styrene resinand polyphenylene ether; and thermoplastic elastomers such as anolefin-based elastomer, a styrene-based elastomer, a urethane-basedelastomer, an amide-based elastomer and a polyester-based elastomer. Onekind of those thermoplastic resins may be used alone, or two or morekinds thereof may be used in combination. In the case where theadditional thermoplastic resin is blended, from the viewpoint offlexibility, the amount of the resin blended is preferably 1 to 900parts by mass with respect to 100 parts by mass of the hydrogenatedblock copolymer.

In the thermoplastic elastomer composition of the present invention, avariety of additives may be blended depending on the intended use inaddition to the above-mentioned components. Examples of the additivesinclude an antioxidant, a light stabilizer, an ultraviolet absorber, alubricant, various fillers, an anti-fogging agent, an anti-blockingagent, a colorant, a flame-retardant, an antistat, a crosslinking agent,a conductivity-imparting agent, an antibacterial agent, an antifungalagent and a foaming agent. Any one kind of those additives may be usedalone, or any two or more kinds thereof may be used in combination. Inthe case where the additive is blended, the amount of the additiveblended is, from the viewpoint of tensile strength, preferably 10 partsby mass or less with respect to 100 parts by mass in total of thehydrogenated block copolymer and non-aromatic rubber softener.

The thermoplastic elastomer composition of the present invention can beproduced by mixing the hydrogenated block copolymer, non-aromatic rubbersoftener and additional components. The mixing can be performed by aconventional method, for example, by mixing the components homogeneouslyusing a mixing device such as a Henschel mixer, a ribbon blender or aV-shaped blender, and melt-kneading the mixture using a kneading devicesuch as a mixing roll, a kneader, a Banbury mixer, a Brabender mixer, ora single-screw or twin-screw extruder. In general, the kneading isperformed at 120 to 300° C.

EXAMPLES

Hereinafter, the present invention is described in more detail by way ofexamples, but is not limited to the examples. It should be noted that,in the examples and comparative examples below, physical properties ofhydrogenated block copolymers and thermoplastic elastomer compositionswere evaluated by the following methods.

(1) Hydrogenation Degree, Styrene Content and Vinyl Bond Amount ValuesWere Calculated from ¹H-NMR Spectra.

-   Device: AVANCE 400 Nanobay (product name, manufactured by BRUKER)-   Solvent: deuterated chloroform-   Measurement temperature: 320 K

(2) Weight-Average Molecular Weight (Mw) and Molecular WeightDistribution (Mw/Mn)

The weight-average molecular weight (Mw), number-average molecularweight (Mn), and molecular weight distribution (Mw/Mn) of a total of acoupled polymer component and an uncoupled polymer component weredetermined in terms of polystyrene by gel permeation chromatography(GPC).

-   Device: GPC-8020 (product name, manufactured by Tosoh Corporation)-   Detector: RI-   Solvent: tetrahydrofuran-   Measurement temperature: 40° C., Flow rate: 1 ml/min-   Injection volume: 150 μl-   Concentration: 5 mg/10 cc (hydrogenated block copolymer/THF)

(3) Coupling Ratio

A coupling ratio was determined from a peak area of the coupled polymercomponent and a peak area of the uncoupled polymer component, obtainedby the GPC.

(4) Branching Index

A branching index was calculated by dividing the weight-averagemolecular weight of the coupled polymer component by the weight-averagemolecular weight of the uncoupled polymer component, obtained by theGPC.

(5) Number of Hydroxyl Groups Contained in Polymer

²⁹Si-NMR measurement was performed for the resultant hydrogenated blockcopolymer, and the number of hydroxyl groups in the polymer wascalculated from a ratio of integrated values of a signal of siliconbonded to a hydroxyl group and a signal of silicon not bonded to ahydroxyl group.

(6) Transition Metal Content

Hydrogenated block copolymers obtained in Examples and ComparativeExamples below were each weighed and heated at 600° C. for 3 hours todecompose organic matter, and the residue was dissolved in an aqueoushydrochloric acid solution, followed by measurement using an atomicabsorption photometer.

Device: Z-6100 (product name, manufactured by Hitachi, Ltd.)

(7) Yellowing

Yellowing of a thermoplastic elastomer composition obtained by kneadingwas confirmed by visual observation.

◯: No yellowing observed

x: Yellowing observed

(8) Compression Set

Compression set was measured in accordance with JIS K 6262. A small testpiece was compressed by 25% and heated at 40° C. for 22 hours. After thecompression had been released, the test piece was allowed to stand stillfor 30 minutes at room temperature, followed by measurement of thethickness of the sample to calculate the compression set.

(9) MFR

An MFR value was measured in accordance with JIS K 7210. Thermoplasticelastomer compositions obtained in Examples and Comparative Examplesbelow were each maintained at 160° C. for 4 minutes, and then the samplewas extruded by applying a load of 21.2 N, followed by measurement ofthe amount of the sample extruded in 10 minutes.

Example 1

Under a nitrogen atmosphere, a dried pressure vessel was charged with3,400 ml of cyclohexane as a solvent and 6.2 ml of sec-butyl lithium ata concentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 107.6 ml of a mixture containing isoprene and butadieneat a mass ratio of 50/50 was added to perform polymerization for 2hours. Subsequently, 177 ml of styrene was added to performpolymerization for 1 hour, and 260 ml of a mixture containing isopreneand butadiene at a mass ratio of 50/50 was added to performpolymerization for 2 hours. Then, the mixture was heated to 70° C., and8.5 g of a solution of 5 wt % bisdiethoxymethylsilylethane (BEMSE) inTHF was added to perform a coupling reaction for 5 hours. Subsequently,0.30 ml of methanol was added to terminate polymerization, to therebyobtain a polymerization reaction solution containing a block copolymer.To the reaction mixture was added 60 ml of cobalt neodecanoate-triethylaluminum (0.0962 mol/L cyclohexane solution) as a hydrogenation catalystto perform a hydrogenation reaction at a hydrogen pressure of 2 MPa and150° C. for 10 hours. After cooling and pressure release, an aqueousphosphoric acid solution was added under an air atmosphere, followed bywashing with water. The resultant product was further vacuum dried toobtain a hydrogenated block copolymer (hereinafter, referred to ashydrogenated block copolymer (R-1)).

The hydrogenated block copolymer (R-1) was found to have a styrenecontent of 39% by mass, a hydrogenation degree of 97.3%, a vinyl bondamount of 5.1%, a weight-average molecular weight of 289,000, a couplingratio of 70%, a branching index of 2.50, a transition metal content of10 ppm, and the number of hydroxyl groups of 1.2.

Example 2

Under a nitrogen atmosphere, a dried pressure vessel was charged with3,400 ml of cyclohexane as a solvent and 6.2 ml of sec-butyl lithium ata concentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 80 ml of a mixture containing isoprene and butadiene ata mass ratio of 50/50 was added to perform polymerization for 2 hours.Subsequently, 233 ml of styrene was added to perform polymerization for1 hour, and 402 ml of a mixture containing isoprene and butadiene at amass ratio of 50/50 was added to perform polymerization for 2 hours.Then, the mixture was heated to 70° C., 13.5 g of a solution of 5 wt %bistriethoxysilylethane (BESE) in THF was added to perform a couplingreaction for 2 hours. Subsequently, 7.0 ml of sec-butyl lithium at thesame concentration mentioned above was added to perform a reaction for 6hours. Then, 0.35 ml of methanol was added to terminate polymerization,to thereby obtain a polymerization reaction solution containing a blockcopolymer. To the reaction mixture was added 60 ml of cobaltneodecanoate-triethyl aluminum (0.0962 mol/L cyclohexane solution) as ahydrogenation catalyst to perform a hydrogenation reaction at a hydrogenpressure of 2 MPa and 150° C. for 10 hours. After cooling and pressurerelease, an aqueous phosphoric acid solution was added under an airatmosphere, followed by washing with water. The resultant product wasfurther vacuum dried to obtain a hydrogenated block copolymer(hereinafter, referred to as hydrogenated block copolymer (R-2)).

The hydrogenated block copolymer (R-2) was found to have a styrenecontent of 40% by mass, a hydrogenation degree of 97.8%, a vinyl bondamount of 4.1%, a weight-average molecular weight of 346,000, a couplingratio of 83%, a branching index of 3.14, a transition metal content of20 ppm, and the number of hydroxyl groups of 0.7.

Example 3

Under a nitrogen atmosphere, a dried pressure vessel was charged with3,400 ml of cyclohexane as a solvent and 7.3 ml of sec-butyl lithium ata concentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 156 ml of a mixture containing isoprene and butadiene ata mass ratio of 50/50 was added to perform polymerization for 2 hours.Subsequently, 257 ml of styrene was added to perform polymerization for1 hour, and 378 ml of a mixture containing isoprene and butadiene at amass ratio of 50/50 was added to perform polymerization for 2 hours.Then, the mixture was heated to 70° C., and 15.0 g of a solution of 5 wt% bistriethoxysilylethane (BESE) in THF was added to perform a couplingreaction for 2 hours. Subsequently, 6.6 ml of t-butyl magnesium bromideat a concentration of 1 mol/L (THF solution) was added to perform areaction for 4 hours. Then, 0.35 ml of methanol was added to terminatepolymerization, to thereby obtain a polymerization reaction solutioncontaining a block copolymer. To the reaction mixture was added 100 mlof cobalt neodecanoate-triethyl aluminum (0.0962 mol/L cyclohexanesolution) as a hydrogenation catalyst to perform a hydrogenationreaction at a hydrogen pressure of 2 MPa and 150° C. for 10 hours. Aftercooling and pressure release, an aqueous phosphoric acid solution wasadded under an air atmosphere, followed by washing with water. Theresultant product was further vacuum dried to obtain a hydrogenatedblock copolymer (hereinafter, referred to as hydrogenated blockcopolymer (R-3)).

The hydrogenated block copolymer (R-3) was found to have a styrenecontent of 44% by mass, a hydrogenation degree of 97.0%, a vinyl bondamount of 3.8%, a weight-average molecular weight of 339,000, a couplingratio of 85%, a branching index of 2.76, a transition metal content of88 ppm, and the number of hydroxyl groups of 0.8.

Example 4

Under a nitrogen atmosphere, a dried vessel was charged with 3,400 ml ofcyclohexane as a solvent and 6.2 ml of sec-butyl lithium at aconcentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 104 ml of a mixture containing isoprene and butadiene ata mass ratio of 50/50 was added to perform polymerization for 2 hours.Subsequently, 184 ml of styrene was added to perform polymerization for1 hour, and 271 ml of a mixture containing isoprene and butadiene at amass ratio of 50/50 was added to perform polymerization for 2 hours.Then, the mixture was heated to 70° C., and 10.5 g of solution of 5 wt %bistriethoxysilylethane (BESE) in THF was added to perform a couplingreaction for 2 hours. Subsequently, 0.20 ml of methanol was added toterminate polymerization, to thereby obtain a polymerization reactionsolution containing a block copolymer. To the reaction mixture was added60 ml of cobalt neodecanoate-triethyl aluminum (0.0962 mol/L cyclohexanesolution) as a hydrogenation catalyst to perform a hydrogenationreaction at a hydrogen pressure of 2 MPa and 150° C. for 10 hours.Further, 6.6 ml of t-butyl magnesium bromide at a concentration of 1mol/L (THF solution) was added to perform a reaction for 2 hours. Aftercooling and pressure release, an aqueous phosphoric acid solution wasadded under an air atmosphere, followed by washing with water. Theresultant product was further vacuum dried to obtain a hydrogenatedblock copolymer (hereinafter, referred to as hydrogenated blockcopolymer (R-4)).

The hydrogenated block copolymer (R-4) was found to have a styrenecontent of 40% by mass, a hydrogenation degree of 97.8%, a vinyl bondamount of 4.5%, a weight-average molecular weight of 267,700, a couplingratio of 80%, a branching index of 2.62, a transition metal content of49 ppm, and the number of hydroxyl groups of 1.3.

Comparative Example 1

Under a nitrogen atmosphere, a dried pressure vessel was charged with3,400 ml of cyclohexane as a solvent and 6.2 ml of sec-butyl lithium ata concentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 130 ml of a mixture containing isoprene and butadiene ata mass ratio of 50/50 was added to perform polymerization for 2 hours.Subsequently, 221 ml of styrene was added to perform polymerization for1 hour, and 326 ml of a mixture containing isoprene and butadiene at amass ratio of 50/50 was added to perform polymerization for 2 hours.Then, the mixture was heated to 70° C., and 12.9 g of a solution of 5 wt% bistriethoxysilylethane (BESE) in THF was added to perform a couplingreaction for 2 hours. Subsequently, 0.3 ml of methanol was added toterminate polymerization, to thereby obtain a polymerization reactionsolution containing a block copolymer. To the reaction mixture was added101 ml of cobalt neodecanoate-triethyl aluminum (0.0962 mol/Lcyclohexane solution) as a hydrogenation catalyst to perform ahydrogenation reaction at a hydrogen pressure of 2 MPa and 150° C. for10 hours. After cooling and pressure release, an aqueous phosphoric acidsolution was added under an air atmosphere, followed by washing withwater. The resultant product was further vacuum dried to obtain ahydrogenated block copolymer (hereinafter, referred to as hydrogenatedblock copolymer (H-1)).

The hydrogenated block copolymer (H-1) was found to have a styrenecontent of 40% by mass, a hydrogenation degree of 96.5%, a vinyl bondamount of 5.4%, a weight-average molecular weight of 339,000, a couplingratio of 85%, a branching index of 2.70, a transition metal content of466 ppm, and the number of hydroxyl groups of 3.4.

Comparative Example 2

Under a nitrogen atmosphere, a dried pressure vessel was charged withcharged 3,400 ml of cyclohexane as a solvent and 6.2 ml of sec-butyllithium at a concentration of 10.5 wt % as an initiator, and the mixturewas heated to 50° C. Then, 80 ml of a mixture containing isoprene andbutadiene at a mass ratio of 50/50 was added to perform polymerizationfor 2 hours. Subsequently, 233 ml of styrene was added to performpolymerization for 1 hour, and 402 ml of a mixture containing isopreneand butadiene at a mass ratio of 50/50 was added to performpolymerization for 2 hours. Then, the mixture was heated to 70° C., and13.5 g of a solution of 5 wt % bistriethoxysilylethane (BESE) in THF wasadded to perform a coupling reaction for 2 hours. Subsequently, 1.8 mlof sec-butyl lithium at a concentration of 10.5 wt % was added toperform a reaction for 6 hours. Then, 0.35 ml of methanol was added toterminate polymerization, to thereby obtain a polymerization reactionsolution containing a block copolymer. To the reaction mixture was added60 ml of cobalt neodecanoate-triethyl aluminum (0.0962 mol/L cyclohexanesolution) as a hydrogenation catalyst to perform a hydrogenationreaction at a hydrogen pressure of 2 MPa and 150° C. for 10 hours. Aftercooling and pressure release, an aqueous phosphoric acid solution wasadded under an air atmosphere, followed by washing with water. Theresultant product was further vacuum dried to obtain a hydrogenatedblock copolymer (hereinafter, referred to as hydrogenated blockcopolymer (H-2)).

The hydrogenated block copolymer (H-2) was found to have a styrenecontent of 40% by mass, a hydrogenation degree of 97.8%, a vinyl bondamount of 4.1%, a weight-average molecular weight of 346,000, a couplingratio of 83%, a branching index of 3.14, a transition metal content of586 ppm, and the number of hydroxyl groups of 1.7.

Comparative Example 3

Under a nitrogen atmosphere, a dried pressure vessel was charged with3,400 ml of cyclohexane as a solvent and 7.2 ml of sec-butyl lithium ata concentration of 10.5 wt % as an initiator, and the mixture was heatedto 50° C. Then, 151 ml of a mixture containing isoprene and butadiene ata mass ratio of 50/50 was added to perform polymerization for 2 hours.Subsequently, 249 ml of styrene was added to perform polymerization for1 hour, and 366 ml of a mixture containing isoprene and butadiene at amass ratio of 50/50 was added to perform polymerization for 2 hours.Then, the mixture was heated to 70° C., and 16.6 g of a solution of 5 wt% tetraethoxysilane (TEOS) in THF was added to perform a couplingreaction for 2 hours. Subsequently, 0.35 ml of methanol was added toterminate polymerization, to thereby obtain a polymerization reactionsolution containing a block copolymer. To the reaction mixture was added60 ml of cobalt neodecanoate-triethyl aluminum (0.0962 mol/L cyclohexanesolution) as a hydrogenation catalyst to perform a hydrogenationreaction at a hydrogen pressure of 2 MPa and 150° C. for 10 hours. Aftercooling and pressure release, an aqueous phosphoric acid solution wasadded under an air atmosphere, followed by washing with water. Theresultant product was further vacuum dried to obtain a hydrogenatedblock copolymer (hereinafter, referred to as hydrogenated blockcopolymer (H-3)).

The hydrogenated block copolymer (H-3) was found to have a styrenecontent of 41% by mass, a hydrogenation degree of 97.4%, a vinyl bondamount of 5.1%, a weight-average molecular weight of 252,700, a couplingratio of 77%, a branching index of 2.38, a transition metal content of518 ppm, and the number of hydroxyl groups of 1.6.

Physical properties of the hydrogenated block copolymers obtained inExamples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1below.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 4 Example 1 Example 2 Example 3 Hydrogenated block copolymerR-1 R-2 R-3 R-4 H-1 H-2 H-3 Coupling agent BEMSE BESE BESE BESE BESEBESE TEOS Steps* α β β γ α β α Molar ratio of deactivating — 1.5 1.0 1.4— 0.39 — reagent/functional group Y remaining after coupling reactionCoupling ratio (%) 70 83 85 80 85 83 77 Branching index (—) 2.50 3.142.76 2.62 2.70 3.14 2.38 Number of hydroxyl groups 1.2 0.7 0.8 1.3 3.41.7 1.6 (group(s)/molecule) Transition metal content (ppm) 10 20 88 49466 586 518 *Steps . . . α: Step (a) → Step (b) → Step (c) β: Step (a) →Step (d) → Step (b) → Step (c) γ: Step (a) → Step (b) → Step (d) → Step(c)

As shown in Table 1, in each of the hydrogenated block copolymersobtained in Examples 1 to 4, the number of hydroxyl groups is 1.5 orless, and the transition metal content is 100 ppm or less. On the otherhand, in each of the hydrogenated block copolymers obtained inComparative Examples 1 to 3, the number of hydroxyl group is 1.5 ormore, so the transition metal content is high.

Examples 5 to 8 and Comparative Examples 4 to 6

The hydrogenated block copolymers (R-1) to (R-4) and (H-1) to (H-3)obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were eachblended with a non-aromatic rubber softener and an antioxidant such that500 parts by mass of the non-aromatic rubber softener was blended withrespect to 100 parts by mass of the hydrogenated block copolymer and theantioxidant was blended at a mass ratio shown in Table 2, and thecomponents were premixed and then melt-kneaded at 170° C. for 5 minutesusing a Brabender mixer. After that, the mixture was pressed into a testpiece for compression set measurement using a press molding machine. Theperformance of the resultant thermoplastic elastomer composition wasevaluated in accordance with the methods (7) to (9) above. The resultsare shown in Table 2. It should be noted that the following productswere used as the non-aromatic rubber softener and antioxidant.

Non-aromatic rubber softener: paraffin-based process oil, product name:Diana process oil PW-32, manufactured by Idemitsu Kosan Co., Ltd.,kinetic viscosity at 40° C.: 30.98 mm²/s

Antioxidant: hindered phenol-based antioxidant, product name: IRGANOX1010, manufactured by Ciba Specialty Chemicals

TABLE 2 Comparative Comparative Comparative Example 5 Example 6 Example7 Example 8 Example 4 Example 5 Example 6 Hydrogenated block copolymerR-1 R-2 R-3 R-4 H-1 H-2 H-3 Additive amount of antioxidant 0.6 0.3 0.50.4 1.4 1.5 1.5 (part(s) by mass) Yellowing ∘ ∘ ∘ ∘ x x x Compressionset (40° C., 22 hr) (%) 22 17 9 20 11 19 16 MFR (160° C., 21.2 N) (g/10min) 178 411 286 520 331 457 490

As shown in Table 2, the thermoplastic elastomer compositions obtainedby kneading in Examples 5 to 8 did not turn yellow because thehydrogenated block copolymers used had low transition metal contents. Onthe other hand, in Comparative Examples 4 to 6, the thermoplasticelastomer compositions obtained by kneading turned yellow because thehydrogenated block copolymers used had high transition metal contents.

INDUSTRIAL APPLICABILITY

Each of the hydrogenated block copolymer obtained by the productionmethod of the present invention and the thermoplastic elastomercomposition containing the copolymer includes no substance which causesenvironmental pollutions or deterioration of the composition, such as atransition metal, and hence can be used effectively in wide range ofapplications such as buffer materials, damping materials, sealants,grips, toys, and sundry articles.

1. A method for producing a hydrogenated block copolymer, the methodcomprising: (A) reacting a living anionic polymer of formula (I):P—X  (I), wherein P is a copolymer chain comprising, in reacted form, anaromatic vinyl compound polymer block (A) and a conjugated diene polymerblock (B) and X is an active terminal of the living anionic polymer,with a coupling agent of formula (II):R¹ _(m)Y_(3-m)Si-A-SiY_(3-m)R¹ _(m)  (II), wherein each R¹ isindependently an aryl group having 6 to 12 carbon atoms, a linear orbranched alkyl group having 1 to 12 carbon atoms, or a hydrogen atom,each Y is independently a fluorine atom, a chlorine atom, a bromineatom, an iodine atom, an alkoxy group, a carboxyl group, or a carboxylicacid ester group, A is a single bond or a linear alkylene group having 1to 20 carbon atoms, and m is 0 or 1, to obtain a block copolymer; (B)hydrogenating the block copolymer, to form a hydrogenated blockcopolymer; and (C) isolating the hydrogenated block copolymer, wherein anumber of functional groups derived from the coupling agent in thehydrogenated block copolymer isolated in (C) is 1.5 or less per blockcopolymer molecule.
 2. The method of claim 1, wherein each Y, in formula(II), is an alkoxy group —OR², wherein each R² is independently a linearor branched alkyl group having 1 to 12 carbon atoms.
 3. The method ofclaim 2, wherein the coupling agent is a bisdialkoxyalkylsilylalkane. 4.The method of claim 3, wherein the coupling agent isbisdiethoxymethylsilylethane.
 5. The method of claim 1, wherein thefunctional groups derived from the coupling agent in the hydrogenatedblock copolymer comprise hydroxyl groups bonded directly to Si atoms. 6.The method of claim 1, further comprising, prior to the isolating: (d)deactivating at least a portion of unreacted functional groups Y presentin a coupling agent residue in the block copolymer or the hydrogenatedblock copolymer.
 7. The method of claim 1, wherein the hydrogenatedblock copolymer has a branching index of 2.3 or more.
 8. A hydrogenatedblock copolymer, comprising: at least one selected from the groupconsisting of a copolymer of formula P′ and a copolymer of formula(P′)_(n)—Z, wherein P′ is a copolymer chain comprising, in reacted form,an aromatic vinyl compound polymer block (A) and a hydrogenatedconjugated diene polymer block (B) and Z is part of a silane couplingagent of formula (II):R¹ _(m)Y_(3-m)Si-A-SiY_(3-m)R¹ _(m)  (II), wherein each R¹ isindependently an aryl group having 6 to 12 carbon atoms, a linear orbranched alkyl group having 1 to 12 carbon atoms, or a hydrogen atom,each Y is independently a fluorine atom, a chlorine atom, a bromineatom, an iodine atom, an alkoxy group, a carboxyl group, or a carboxylicacid ester group, A is a single bond or a linear alkylene group having 1to 20 carbon atoms, m is 0 or 1, and n is an integer of 1 to 6, whereinthe hydrogenated block copolymer has a branching index of 2.3 or moreand a transition metal content of 100 ppm or less.
 9. The hydrogenatedblock copolymer of claim 8, obtained by a method comprising: (A)reacting a living anionic polymer of formula (I):P′—X  (I), wherein P′ is a copolymer chain comprising the aromatic vinylcompound polymer block (A) and the conjugated diene polymer block (B)and X is an active terminal of the living anionic polymer, with acoupling agent of formula (II), to obtain a block copolymer; (B)hydrogenating the block copolymer, to form a hydrogenated blockcopolymer; and (C) isolating the hydrogenated block copolymer, wherein anumber of functional groups derived from the coupling agent in thehydrogenated block copolymer isolated in (C) is 1.5 or less per blockcopolymer molecule.
 10. A thermoplastic elastomer composition,comprising: the hydrogenated block copolymer of claim 8; and anon-aromatic rubber softener at a ratio of 1 to 2,000 parts by mass withrespect to 100 parts by mass of the hydrogenated block copolymer. 11.The method of claim 1, wherein the polymer block (A) comprises, inreacted form, at least one aromatic vinyl compound selected from thegroup consisting of styrene, α-methylstyrene, 2-methylstyrene,3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene,4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene,1-vinylnaphthalene and 2-vinylnaphthalene.
 12. The method of claim 11,wherein the polymer block (A) comprises styrene.
 13. The method of claim11, wherein the polymer block (A) comprises α-methylstyrene.
 14. Themethod of claim 1, wherein the polymer block (B) comprises, in reactedform, at least one conjugated diene selected from the group consistingof 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,and 1,3-hexadiene.
 15. The method of claim 14, wherein the polymer block(B) comprises, in reacted form, 1,3-butadiene and isoprene.
 16. Themethod of claim 2, wherein the coupling agent is abistrialkoxysilylalkane.
 17. The method of claim 16, wherein thecoupling agent is bistriethoxysilylethane.
 18. The hydrogenated blockcopolymer of claim 8, having a branching index of 2.4 or more and atransition metal content of 80 ppm or less.
 19. The hydrogenated blockcopolymer of claim 18, having a branching index of 2.6 or more.
 20. Thehydrogenated block copolymer of claim 18, having a transition metalcontent of 50 ppm or less.